DIGESTION. 55 



%. That they may be nourished, all living beings require that 

 alimentary substance should be introduced into their bodies frorp 

 time to time. 



4. Plants pump up by their roots the aliments furnished them by 

 the earth, and these matters are mingled with the nutritious liquid 

 called &/;, which permeates throughout their tissues without having 

 undergone any preparation. 



5. With animals it is altogether different. The aliments, pre- 

 viously to being absorbed and diffused through the different parts 

 of the body, to afford nourishment to the organs, and to enter 

 into the composition of their tissues, have to undergo a certain pro- 

 cess of preparation, called din cut ion. 



6. Digestion has for its object : 



1st To separate from alimentary substances the nutritive part 

 from that which is not. 



2nd. To transform this nutritive part into a peculiar liquid, fit 

 to mix with the blood and nourish the organs, which liquid is called 

 ckt,l<>. 



7. The process of digestion always takes place in a cavity situ- 

 ated in the interior of the body and communicating externally in 

 such a way that aliments may enter it. 



8. All animals are provided with a triffestivr tavity. 



9. Plants, on the contrary, having no need to digest ali- 

 ments, have no such cavity. [The alimentary surface of a plant 

 is the exterior of its root spread out in the earth.] 



1 0. In some animals the digestive cavity is simply a pouch, com- 

 municating externally by a single opening, which performs the 

 functions both of a mouth arid of an anus. 



1 1. But with the greatest number it is otherwise. The diges- 

 tive cavity has the form of a tube, open at its two ends ana 

 enlarged about the middle. This enlarged portion of the diges- 

 tive tube is named stomach-, and serves to contain the aliments, 

 while the greatest part of the process of digestion Is performed. 



3. That living beings may be nourished, what circumstance is neces. 

 eary ? 



4. Do the nutritious fluids, received by p'ants from the earth, undergo any 

 process of preparation or digestion ? 



5. In order to nourish animal organs, is it sufficient to introduce food 

 int i the stomach ? 



6. What is the object of f'igesiion ? What is chyle? 



7. Where does digestion take place ? 



8. Have all animals a digest ve cavity ? 



9. Why have plants no digestive cavity? 



10. What is the nature of the digestiv ca ity in some ammais? 



11. What is the for n o' the dig stive cavity m the g eatest number o* 

 animals ? What part is called the- stomach ? 



